In applications having critical noise in heavy duty transmissions, topologically corrected gears modified in their surface structure are increasingly being used. The noise behavior of known transmissions is decisively influenced by the excitation from the gear provided. This influence of the gear geometry on the excitation behavior is explained by specific main geometry characteristics such as the profile and the overlap ratio as well as by the shape of the tooth flank topology. In addition, any even only slight production deviation from the fixed tooth flank geometry can have a negative effect on the excitation behavior.
It is currently being endeavored to optimize the excitation behavior with specific flank corrections in order thus to improve the noise behavior of certain types of transmission.
With gears having critical noise, a waviness can in this respect be specifically desired on the tooth flank to reduce or to prevent the noise excitation behavior of the gear wheel pairing.
It is the object of the present disclosure to provide the skilled person with a method for the manufacture of a workpiece having a modified surface structure and a corrected gear geometry which generates a modification, in particular a profile modification or profile waviness and/or a defined periodic flank waviness, on the active surface of the workpiece machined therewith or modifies or prevents an unwanted flank waviness.
This object is achieved by a method of manufacturing a workpiece in accordance with a method for the manufacture of a workpiece in particular by generation grinding or gear honing in which it is achieved by a specific generation of a wobble movement and/or of an eccentricity of the grinding tool or honing tool that a modification, in particular a profile modification or profile waviness and/or a defined periodic flank waviness, is generated on the active surface of the workpiece ground or honed therewith.
The profile modification in accordance with the present disclosure can in particular be utilized to generate a desired flank waviness on the active surface of the workpiece.
The profile modification in accordance with the present disclosure, however, likewise makes it possible to measure a periodic flank waviness at a finished workpiece and to compensate it by an oppositely directed correction in accordance with the method in accordance with the present disclosure, to modify it and/or to provide these corrections in the machining of further workpieces.
In accordance with the present disclosure, in this respect in a first embodiment for the manufacture of a workpiece having a corrected gear geometry and a modified surface structure a method is proposed for balancing the corresponding grinding tool in which a periodic flank waviness on the active surface of the ground workpiece is generated by a specific setting of a tool balance or tool imbalance. The surface geometry of the machined workpiece is thereby matched to the resulting demands.
Alternatively, the dresser for the tool can be controlled so that the tool surface of the grinding tool or honing tool is given a corresponding structure which generates a comparable surface geometry at the machined workpiece in a subsequent machining process.
The dressing tool can in particular be controlled in the dressing and profiling of the hard finishing tool so that a preferably periodic flank waviness is generated on the surface of the tool which in turn generates a comparable periodic flank waviness on the active surface of the workpieces ground/honed therewith.
The tool modified in its balance/imbalance and/or surface structure is in particular suitable for grinding or honing cylindrical spur gearing arrangements or helical gearing arrangements having a corrected gear geometry and a modified surface structure. These corrections can be superimposed on the correction movements such as correspond to the hard finishing of gears from the prior art. This also applies e.g. to spherical or conical gears such as beveloid gears.
The tool is in principle a worm grinding wheel or a honing ring or an externally toothed honing tool whose surface structure is dressed and profiled using a method of the prior art.
An imbalance, above all at the grinding tool, can have a plurality of reasons. A plurality of possibilities thus also arise to set or generate the balance/imbalance directly. Possible causes for an imbalance are e.g. the tool attachment, the tool design or its configuration and/or density differences in the tool blank. In addition, the imbalance can have its cause in the tools or in use at the reception capacity for cooling lubricant distributed differently over the periphery.
As a rule, the tools are balanced statically and dynamically on external balancing machines in the new state. For this purpose, balance weights which are attached laterally next to the tools are displaced for so long until the desired balance quality is achieved. This balancing can take place in one or two planes depending on the tool dimensions.
In addition, the tools are periodically dressed later in operation after a defined number of workpieces was machined by the tool and the tool therefore has to be dressed again. For this purpose, balancing heads are installed in the gear cutting machines or in the tool mounts which can be adjusted using an NC control in order thus to carry out the fine balancing within the machine.
Different points in time at which influence can be taken on the balancing quality or at which it is meaningful to set the balancing quality of the tool in accordance with the present disclosure result from these two balancing methods/balancing processes.
With new tools, the cause for the tool imbalance can also lie in an off-center tool attachment since the bore of the tool usually has a clearance, albeit a small one, with respect to the receiving mandrel. This eccentricity of the attachment mainly has the effect of a static imbalance. The tool run-out error resulting from the alignment state is eliminated in the subsequent first dressing in the machine. Since this in turn has effects on the balancing quality, this imbalance is preferably corrected on the external balancing machine and is only utilized in exceptional cases for the balance setting in accordance with the present disclosure.
The situation is different with the imbalance from the grinding tool configuration. There are better possibilities to set the balance/imbalance directly here.
The teeth at the grinding tool extend in helical form around the tool axis. The tool pitches end at an offset angle in the outer diameter of the worm grinding wheel in dependence on the tool width and tool module. If the pitches end offset by zero degrees, a dynamic imbalance arises; at an offset of 180 degrees, the consequence is a static imbalance. If the worm pitches end at intermediate angular positions, a combination of static and dynamic imbalance results. This influence only applies with single-pitch worm grinding wheels.
Up to now, the useful worm width of the cylindrical worm grinding wheel blank has usually been selected so that the dynamic imbalance caused by pitch geometry becomes minimal.
In line with the present disclosure, the width can now, however, also be selected directly in the manufacture of the new tool such that the pitch ends of the worm grinding wheel are arranged at different angular positions at the outer tool diameter and thus the grinding tool has a defined dynamic basic balance/imbalance inherent in the system.
Provision can alternatively or additionally be made that the tool is balanced on the grinding machine to provide the desired defined imbalance. A balancing head is advantageously installed for this purpose in the grinding machine or in the tool mount and can be adjusted by NC control in order thus to carry out the fine balancing within the machine.
The setting of the imbalance on the machine in this respect advantageously takes place periodically during the grinding operation. This is sensible in this respect since a rebalancing will always be necessary in the grinding process since the tool changes constantly by the periodic dressing process and the balance is also influenced in the grinding process by the reception of cooling lubricant.
The influence on the tool configuration can in particular be directly amplified or reduced in the rebalancing on the grinding machine by additional dynamic “changing/altering of the basic balance/imbalance.
A further possibility of generating periodic flank waviness in the machined workpieces comprises modifying the surface of the tool directly during the dressing and profiling process so that the desired surface geometry is generated in the workpieces machined therewith or an existing unwanted surface geometry is prevented.
This modification can be carried out instead or of in addition to the wobble movement of the tool.
In the following formulaeIndex 1=toolIndex 2=workpieceapplies.
The desired modification of the surface geometry of the workpiece on the gear flank can in particular have a constant value in the generation pattern at least locally in a first direction (GC2) of the workpiece and can be given by a function f(x) in a second direction of the workpiece which extends perpendicular to the first direction (GC2).
In this respect, in particular the first direction (GC2) and the function f(x) can be predefined, for example for defining a desired modification or for compensating a measured, unwanted modification.
In this case, in accordance with the present disclosure, a modification of the surface geometry or the tool can be used for producing this modification of the surface geometry of the workpiece which likewise has a constant value at least locally in the generation pattern in a first direction (GC1) of the tool.
A modification of the surface geometry of the tool is preferably used which is given at least locally by the same function, optionally compressed linearly by a factor c, f(cx) in a second direction of the tool which extends perpendicular to the first direction (GC1).
In this respect, the geometry of the workpiece and the tool in a first embodiment in the generation pattern cannot only be described locally and/or in a partial region of the generation pattern, but also globally by the above-given formulae. In this case, the lines along which the modification has a constant value each form a straight line over the whole generation pattern or can be approximated by such with small differences.
Provision can, however, alternatively be made that the line along which the modification has a constant value does not form a straight line in the workpiece and/or in the tool, but is rather curved and/or has a plurality of part regions which do not extend in straight lines with respect to one another. In this case, the generation pattern can, however, be approximated in accordance with the present disclosure locally at at least one point by the above-described formulae and can preferably be approximated in each case locally by the above-described formulae preferably along the line or in partial regions. Optionally, in this respect, the function f( ) respectively have a different form for different regions along such a line.
The generation pattern then optionally has to be composed of a plurality of part regions described by formulae in accordance with the present disclosure.
The modification of the surface geometry is preferably defined by the formula:f(2*pi/lambda2*cos(psi2)*L2−2*pi/lambda2*sin(psi2)*b2).
This formula also applies when unwanted flank waviness arises in the hard finishing process which can, however, be compensated by using this method.
Here f is a real-valued function which does not have to be periodic. f=sin can be selected in order to generate waviness, for example. The angle psi2 defines the direction of a straight line (GC2) on the gear flank on which the modification has a constant value. The modification has a form of f( ) along the straight line in every other direction.
It is compressed differently along the straight line in dependence on the direction. The compression is at a maximum (with waviness, the wavelength is minimal) on the straight line perpendicular to GC2.
The Factor:2*pi/lambda2 determines the compression of the modification along the straight line perpendicular to GC2.
For waviness, lambda2 corresponds to the wavelength along the straight line parallel to GC2. For the straight lines along a constant gear width, the compression amounts to:2*pi/lambda2*cos(psi2)(with waviness,the wavelength is lambda2/cos(psi2)),for straight lines along a constant generation length, the compression amounts to:2*pi/lambda2*sin(psi2)(with waviness,the wavelength is lambda2/cos(psi2)).
These formulae also apply, as already explained above, at least locally and/or in a partial region of the generation pattern; however, globally in a particularly simple case.
A modification, in particular a modification corresponding to the above-described modification of the workpiece, can be generated on the tool surface by dressing the tool (worm, honing wheel/honing ring) using a form roller. This can be achieved by one or more of the following corrections of the axial movements for conventional dressing kinematics:                a. Variation of the axial spacing of the dresser from the tool in dependence on the angle of rotation of the tool or on the tool width (infeed);        b. Variation of the axial feed of the tool or of the dresser in dependence on the angle of rotation of the tool or on the tool width (shift);        c. Variation of the crossed-axis angle of the tool and of the dresser in dependence on the angle of rotation of the tool or on the tool width (pivot); and        d. Variation of the tool speed in dependence on the angle of rotation of the tool or on the tool width.        
The form roller can in this respect in particular be in contact with the tooth of the tool from the base region to the crest region during dressing so that the eccentric modification takes place in one stroke over the whole tooth height.
Alternatively, the form roller can be in contact with the tooth of the tool only in partial regions between the base and the crest during dressing so that the eccentric modification takes place in several strokes (movement of the dressing roller in the direction of the tool axis) over the whole tooth height and with a respective different relative positioning of the dresser.
A modification of the typef(2*pi/lambda1*cos(psi2)*L2−2*pi/lambda1*sin(psi1)*b1).can be generated on the tool by dressing with a form roller since the contact line of the dresser and of the tool, shown in a generation path-width diagram, is approximately a straight line. This straight line defines the straight line Gc1 (and thus the angle psi1) since the corrections of the dressing kinematics have approximately the same effect on all points which lie along Gc1 and are thus dressed simultaneously. The contact line migrates along the tooth flank in the width direction during dressing.
If the contact line of the dresser and of the tool in contrast differs greatly from a straight line, the formula given above only applies locally or in partial regions of the contact line. The generation pattern then optionally has to be composed of a plurality of part regions described by formulae in accordance with the present disclosure.
If the dressing kinematics are varied so that a modification of the formf(−2*pi/lambda1*sin(psi1)*b1)results along the contact line on the tool, the desired modification arises over the flank of the tool.
Such a modification can be superimposed with other modifications (e.g. convexities) on the dressing of the tool.
It two involute spur gears mesh at crossed axial angles, the flanks only contact one another at one point.
In the generation path-width diagram, the contact points each move on a straight line (G1 or G2). If the tool has a modification off(2*pi/lambda1*cos(psi1)*L1−2*pi/lambda1*sin(psi1)*b1)a point on G1, as discussed above, is a modification of the form f( ). The compression of the modification depends on lambda1 and psi1 and on the direction G1.
Each point on G1 images its modification on the corresponding point on G2. A modification of the form f( ) along G2 thus likewise arises on the workpiece. Its compression depends on lambda1, psi1 and on the direction of G1 and G2.
The directions can be influenced both via the macrogeometry of the tool (pitch number/tooth number, base module, base helix angle), that is also via the respective axial feeds (shift movement). The compression of (f) along G2 can be set by a correct choice of these parameters so that it corresponds to the desired modification on the workpiece.
In accordance with the present disclosure, the macrogeometry of the tool and/or the line of engagement of the dressing tool and/or the axial feed of the workpiece and/or the shift movement of the tool and/or the compression factor c are selected in particular so that the modification of the tool along a line G1 on which the contact point moves on the machining of the workpiece on the tool corresponds to the desired modification of the workpiece along a line G2 on which the contact point moves on the workpiece.
This corresponds to the demand that the parameters of the method are selected so that the arguments of the function f( ) on the lines G1 and G2 in the points which contact one another in the machining have the same phasing.
In accordance with the present disclosure, with a predefined macrogeometry of the tool and line of engagement of the dressing tool, the axial feed of the workpiece and/or the shift movement of the tool and/or the compression factor c can in particular be selected accordingly in this respect.
Work is particularly preferably carried out in this respect with an axial feed of the workpiece which is usually otherwise predefined by the machining process, whereas the shift movement of the tool and/or the compression factor c are selected in accordance with the present disclosure to satisfy the above-named condition.
In this respect, a value of the axial feed constant with respect to the workpiece rotation and/or a value of the shift movement constant with respect to the tool rotation can be selected.
Each tooth of the workpiece comes into engagement again and again with the same pitch/tooth of the tool during the process. Continuously different points contact one another in this respect due to the axial feed. It must be ensured that the modification on the worm corresponds to the desired modification on the gear on each engagement. It is sufficient for this purpose to ensure this for the first following engagement and then also only for one contact point. For this purpose, the macrogeometry of the tool and the axial feeds can again be adapted.
In accordance with the present disclosure, the macrogeometry of the tool and/or the line of engagement of the dressing tool and/or the axial feed of the workpiece and/or the shift movement of the tool and/or the compression factor c can therefore in particular be selected so that the modifications of the tool and of the workpiece also correspond along the lines G1′, and G2′ on which the contact points move on the machining of the same tooth of the workpiece with the same pitch of the tool at a later time of the machining process, with these lines being displaced by the axial feed of the workpiece and optionally by the shifting of the tool with respect to the lines G1 and G2.
In this respect, with a predefined macrogeometry of the tool and line of engagement of the dressing tool, the axial feed of the workpiece and/or the shift movement of the tool and/or the compression factor c are in turn preferably selected accordingly.
In addition, with a predefined axial feed of the workpiece, the shift movement of the tool and/or the compression factor c are particularly preferably selected accordingly.
Since on generation grinding or on honing, a linear correlation exists between the generation patterns of the tool and of the workpiece which can be described mathematically, the process parameters for the machining described in more detail above can be mathematically determined via this correlation.
The present disclosure in this respect further comprises a computer program with memory having stored therein an input function for inputting data on a desired modification of the workpiece and having a function for determining the macrogeometry of the tool and/or of the line of engagement of the dressing tool and/or the axial feed of the workpiece and/or the shift movement of the tool and/or of the compression factor c in a manner such that the modification of the tool along a line G1 on which the contact point moves in the machining of the workpiece on the tool corresponds to the desired modification of the workpiece along a line G2 on which the contact point on the workpiece moves.
The computer program can in this respect in particular be suitable for installation on a gear cutting machine or can be installed on same. The parameters determined by the computer program can in particular then be used directly for controlling the gear cutting machine on the dressing and/or machining of a workpiece.
The computer program can, however, also be installed on an external computer. It then advantageously has an output function for data which can be used for controlling a gear cutting machine.
The computer program is in particular set up in this respect so that it implements the above-described functions of the method in accordance with the present disclosure.
The input function can in particular in this respect allow the inputting of data on the first direction (GC2) of the workpiece in which the modification has a constant value and/or on the function f(x) which defines the extent of the modification in a second direction of the workpiece which extends perpendicular to the first direction (GC2).
Further advantageously, the input function can furthermore allow the inputting of data on the macrogeometry of the tool and/or the line of engagement of the dressing tool and/or on the axial feed of the workpiece and/or on the shift movement of the tool, particularly preferably data on the macrogeometry of the tool and on the line of engagement of the dressing tool and optionally on the axial feed of the workpiece.
The computer program in this respect preferably calculates the shift movement of the tool and/or the compression factor c on the basis of the input data.
With the tool set or modified in this manner, the workpieces can then be machined and the desired profile waviness can thus be generated at the ground workpiece or an unwanted waviness present at the workpiece can be measured and can optionally also be corrected by reversing the process. The workpieces can then be processed in grinding in the axial or diagonal process. When honing, the machining processes in accordance with the prior art can be used.
Both single-start and multi-start tools can be considered as tools which are modified in accordance with the present disclosure. In this respect, the tools are in particular a worm grinding wheel or a honing tool.
Some correlations and procedures which, where not otherwise stated, are used both in the first aspect of the present disclosure, i.e., in the specific use of an imbalance, and in the second aspect, i.e., in the specific eccentric modification of the tool, will now be presented generally again in the following.
In the axial grinding process the tool movement takes place parallel or approximate to the workpiece axis of the workpiece. The structure of the flank surface which was machined using a tool in accordance with the present disclosure receives a profile waviness which remains almost the same in the width direction in this respect. This waviness in the profile extends parallel to the tooth base and to the tooth head.
If the tool is additionally shifted in the direction of the tool axis, in this diagonal grinding process the flank modification or flank waviness is also offset obliquely on the flank over the workpiece width in dependence on the engagement conditions. The extent of the slant can be determined via the shift direction (with the rotary movement of the workpiece or opposite thereto).
The method in accordance with the present disclosure can therefore furthermore comprise the steps: Defining a desired alignment of the periodic flank modification; and moving the grinding tool continuously in the axial direction of the workpiece and/or shifting the grinding tool tangentially to the workpiece to obtain the desired alignment of the flank modification.
In a further embodiment of the present disclosure, the tool can also be eccentrically dressed in order thus preferably to generate a profile modification or profile waviness on the flank of the gear in the diagonal grinding process (shift movement of the tool in the axial direction of the tool). These tools can then be set by the balancing on the machine so that no vibrations arise from the tool rotation or the balancing can additionally be utilized in order also to induce micromovements of the tool here again in addition to the eccentricity movements of the tool surface.
The eccentric dressing of the tool in this respect takes place in that the dresser is fed in more or less in dependence on the angular position of the tool or in that the tool is fed in more or less toward the dresser in dependence on the angular position of the tool or vice versa. Since the speed of the tool in dressing is currently usually lower than in the actual machining process, the dynamic demands on the infeed axis for the tool are not as high as if the infeed movement itself were to take place during the machining process by a radial infeed of the tool toward the workpiece. This radial infeed movement would then have to be controlled in dependence on the angular position of the tool in this respect.
On single-flank dressing, it is furthermore conceivable to generate the infeed movement via an additional axial movement in the axial direction of the tool, which takes place in dependence on the angular position of the tool.
In principle, with highly dynamic grinding machines it is, however, also conceivable with a round-dressed grinding tool to generate movements on the workpiece by radial movements of the grinding tool which correspond to a movement of the tool surface of an eccentrically dressed grinding tool. Optionally, an additional second, highly dynamic infeed axle, which is seated on the first radial infeed axle, could also be used for generating these radial movements.
The method in accordance with the present disclosure can therefore furthermore comprise the steps: Defining a desired amplitude of the periodic flank modification; and direct setting of an imbalance and/or of an eccentricity of the tool for manufacturing a workpiece with the desired flank modification.
The magnitude of the infeed movement or of the eccentricity in this respect lies in the micrometer range since the amplitude of the structures or waviness on the tooth flank likewise only lie in the micrometer range.
The desired amplitude of the periodic flank modification in this respect advantageously amounts up to 7 micrometers in particular between 1 and 5 micrometers.
Further advantageously, the amplitude of the dressing-induced or imbalance-induced eccentricity of the tool used in the method in accordance with the present disclosure lies in this respect between 2 micrometers and 20 micrometers, in particular between 3 and 15 micrometers.
The method in accordance with the present disclosure can therefore furthermore comprise the steps: Defining a desired frequency of the periodic flank modification; and modification of the angle of engagement αn0 at the grinding tool for manufacturing a workpiece with the desired flank modification.
The present disclosure further comprises a grinding tool for carrying out a method in accordance with the present disclosure, with the tool being out-of-round-dressed in at least a partial region. In this respect, the tool can have at least two different grinding regions, in particular at least one roughing region and at least one out-of-round dressed finishing region.
The present disclosure further comprises a worm grinding wheel for the carrying out of a method in accordance with the present disclosure, characterized in that the pitch ends of the worm pitches at the two ends of the worm grinding wheel are arranged at different angular positions at the outer periphery.
The present disclosure further comprises a gear cutting machine for carrying out the method in accordance with the present disclosure for balancing and/or for eccentrically dressing a tool, in particular for dressing a tool in accordance with the formulae set forth above. The gear cutting machine can furthermore be suitable for producing a workpiece in accordance with the method in accordance with the present disclosure. It is particularly preferred if all the methods can be carried out in mutual coordination on the gear cutting machine.
The gear cutting machine can in this respect comprise an input function via which a desired amplitude of the periodic flank modification can be predefined and a control function which determines the imbalance and/or eccentricity required to provide the flank modification and sets it for the hard finishing of a workpiece with the desired flank modification.
The gear cutting machine can alternatively or additionally comprise an input function via which a desired imbalance and/or eccentricity can be predefined and a control function which sets the desired imbalance for machining a workpiece with the desired flank modification.
The gear cutting machine can in this respect in particular have a balancing function via which the required imbalance can be set.
The gear-cutting machine can alternatively or additionally have a function for generating a desired modification of the workpiece by an eccentrically dressed tool.
The present disclosure furthermore comprises a gear cutting machine having a machining function which sets the engagement depth of the tool into the workpiece in dependence on the angle of rotation of the tool.
The present disclosure further comprises a gear cutting machine for dressing a hard finishing tool, in particular a worm grinding wheel or a honing tool, having a dressing tool, wherein the gear cutting machine has a function for the out-of-round dressing of the tool which advantageously sets the engagement depth of the dressing tool into the tool in dependence on the angle of rotation of the tool.
Further advantages and properties of the present disclosure will be explained in more detail in the following with reference to the drawings.